Distributor-type fuel injection pump

ABSTRACT

A fuel injection pump of the distributor type which has a reciprocatingly driven pump piston that is load-bearing in a rotating distributor shaft which pumps fuel out of a pump work chamber to various fuel injection valves via a distributor opening. To control the duration of high-pressure injection, an electrically actuated valve is provided with a valve member in a valve chamber that communicates with the pump work chamber and from a second valve chamber, communicates with a low-pressure region. To terminate the high-pressure injection, the valve member makes a communication between the two valve chambers, whereupon the outflow of the fuel stream is controlled by disposing a diameter constriction in the connecting line, thus reducing any tendency to cavitation.

PRIOR ART

The invention is based on a fuel injection pump. In one such fuelinjection pump, known from International Patent Disclosure WO 95/02760,a plurality of pump pistons located crosswise to the direction ofrotation of the distributor are provided, in the manner of a radialpiston pump with a pump work chamber enclosed between them. Theconnecting line used to supply fuel to the pump work chamber and torelieve it has a constant, unthrottled cross section in this known fuelinjection pump. In these pumps, fuel is aspirated with the valve openover the entire intake stroke of the pump pistons, and the valve is thenclosed again to define the effective pumping stroke of the pump pistons.For a particular rotary angle range or time segment, the fuel injectionpump then pumps fuel, which is brought to high injection pressure, toone fuel injection valve at a time, depending on the position of thedistributor. To terminate this pumping or define the fuel injectionquantity, the valve is opened again. In this process the pressure in thepump work chamber, which until now was at a very high level, such as1000 to 1200 bar, is reduced via the valve opening to the low-pressureregion, in that fuel flows out there and at the same time the remainingquantity pumped by the pump piston is forced out. In this relief,because of the major pressure difference between the high- andlow-pressure region, flow separations and flow recirculation zones canarise, and gas bubbles are formed in the fuel which in regions ofrelatively high pressures upon the ensuing implosion lead to materialdamage and so-called cavitation erosion, especially in the vicinity ofthe surrounding walls. Over the long term, this can cause functionalproblems in the fuel injection pump, especially if these erosions extendto the valve seats themselves.

ADVANTAGES OF THE INVENTION

The fuel injection pump of the invention has the advantage over theprior art that because of the diameter constriction in the connectingline, the effects that trip cavitation erosion are suppressed. Becauseof the diameter constriction, the outflow of fuel is throttled to acertain extent or at least in such a way that the fuel flowing out viathe valve opening is rapidly opposed by a certain counterpressure, sothat beyond the valve seat the outflowing fuel cannot expand, whichwould allow an unfavorable flow and would allow gas bubbles to form inthe fuel. Before a continuous flow has built up in the outflow directionvia the connecting line, the diameter constriction instantaneously makesa high throttling action available, which leads to a rapid pressurebuildup in the second valve chamber.

In a further advantageous feature, the connecting line is oriented withits axis in the direction of the valve member, so that in this way afuel exchange between the low-pressure region and the pump work chamberand vice versa can be effected in a streamlined way. Especiallyadvantageously, in, the diameter constriction is designed such that itpromotes a flow of fuel from the low-pressure region to the valveopening or the pump work chamber. The funnel-like design assures thatthe pump work chamber is supplied adequately and quickly with fuelduring the intake phase of the distributor injection pump, without thediameter constriction having a harmful effect on the extent to which thepump work chamber is filled. Advantageously, the transitions on theinflow side to the pump work chamber can also be rounded. The embodimentas a diffusor allows further improvement in flow conditions. In theopposite direction, that is, for the emergence of fuel from the pumpwork chamber toward the low-pressure region, such provisions are notcontemplated, in particular so that the initial throttling, while theflow through the connecting line has not yet been established, will bepreserved in order to reduce the development of gas bubbles.

In a further advantageous feature, a plurality of connecting lines areprovided, so that the above-described instantaneous counterpressure canbuild up uniformly to terminate the high-pressure injection directlyafter the reopening of the valve member, thus averting the formation ofinsular areas of gas bubbles. It is advantageous in this respect if oneof the connecting lines is disposed opposite the pressure conduitleading away from the first valve chamber, so that the quantity of fuelflowing from the first pressure conduit into the second valve chambervia the valve opening will directly meet the throttled outlet from oneof the connecting lines. In all cases, for forming the counterpressureit is important for a compensation piston to be disposed on the valveclosing member, connected to the valve closing member vi a connectingtang and together with the second valve chamber forming an annularchamber. The chamber thus enclosed promotes the development ofcounterpressure and thus serves to reduce the tendency to cavitation.

BRIEF DESCRIPTION OF THE DRAWINGS

One exemplary embodiment of the invention is shown in the drawing andwill be described in further detail below;

FIG. 1 shows a section through a distributor injection pump inaccordance with the standard technology;

FIG. 2 is a partial cross sectional view of the essential part of anelectrically controlled switching valve with a disposition according tothe invention of an embodiment of a connecting line; and

FIG. 3, is a section through the exemplary embodiment of FIG. 2 takenalong the line III—III.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The fuel injection pump of the distributor type, shown in longitudinalsection in fragmentary form in FIG. 1 of the drawing has a pump housing,not visible here, that is closed off in liquid-tight fashion by a pumphead 10. A low-pressure region 45, not described further, is thusenclosed between the pump housing and the pump head and is at the sametime a low-pressure supply region. A cylinder liner 14 is inserted intothe pump head 10 and serves with its inner bore 22 to support adistributor shaft 11. The distributor shaft is driven to rotate by adrive shaft, not further shown, via a slaving means 12 and is supportedso as to be fixed in the axial direction. In the region of a collar 9protruding into the low-pressure region 45, there is at least onetransverse bore 25, in which pump pistons 17 that between them enclose apump work chamber 18 are supported. The pump pistons are driven toexecute a supply stroke inward in the direction of the pump chamber 18by a cam ring, not shown further here, that circumferentially surroundsthem, and they can execute an intake stroke, moving outward on anoutward edge of the cam. The pump work chamber 18 communicatescontinuously via a feed line 19 with a distributor opening 20 in thejacket face of the distributor shaft and is normally covered by thejacket face of the inner bore 22 of the cylinder liner 14. In the regionof this distributor opening, injection lines 21 lead with a rotationalangle offset away from the inner bore 22 of the cylinder line andoptionally communicate via a pressure valve 13 with fuel injectionvalves, not shown further here.

Also leading away from the distributor opening 20 is a pressure conduit46 to a first valve chamber 36, which surrounds part of a valve member35. The valve member has a guide part 37 that is guided in a guide borepart 38, and this guide bore part 38 is part of a recess made coaxiallyinto the distributor shaft from its face end 39. The valve member 35 isaxially movable in the guide part 37 and with the guide part 37 closesoff the first valve chamber 36, adjoining the guide bore part 38, fromthe outside. It should be pointed out in this respect that the part ofthe distributor shaft that carries the face end 39 protrudes out of thecylinder liner and adjoins the low-pressure region. An electromagneticactuating member 16 is located on this side of the cylinder line 14 ordistributor shaft 11; it has an armature 54, a magnet coil 49, whichupon being excited pulls this armature against a magnet core, and atappet 51, which is connected to the armature 54 and acts coaxially onthe valve member 35. The housing of the electromagnetic actuating member16, together with the distributor shaft and the cylinder liner 14,encloses a chamber in the pump head 10 that communicates constantly withthe low-pressure region 45 via a conduit 8.

The valve member 35 has a valve sealing face 32, which comes to rest ona valve seat 34 under the influence of the magnetic force of theelectromagnetic actuating member 16. In this process the valve membercloses a valve opening 32, surrounded by the valve seat 34, that formsthe communication between the first valve chamber 36 and a second valvechamber 24. In the closing direction of the valve member 35, this secondvalve chamber 24 is defined on one side by the valve member 35 and onthe other by a compensation piston 43, which slides in a guide 26adjoining the second valve chamber 24 and on its face end defines aspring chamber 23, in which a spring 44 is disposed that urges the valvemember 35 in the opening direction. The spring chamber ispressure-relieved, in a manner not shown in further detail. Via aconnecting tang 56, the compensation piston 43 is integrally connectedto the valve member 35 in such a way that the second valve chamber is inthe form of an annular chamber. From it, a connecting line 27 leads viaa longitudinal groove 28 to an annular groove 29 in the jacket face ofthe distributor shaft, which in turn communicates constantly with aradial bore 30 in the cylinder line 40, which communicates with a bore31 discharging into the low-pressure region 45. The second valve chamber24 is thus constantly relieved to the low-pressure region 45.

In operation of the distributor injection pump, the valve member 35 isopen during the intake stroke of the pump pistons 17, so that via theabove-described communication, fuel can flow out of the low-pressureregion 45 via the first valve chamber 36, the pressure conduit 46, thedistributor opening 20 and the feed line 19, to reach the pump workchamber 18. Beyond a certain time in the inward motion of the pumppistons 17, which is the desired injection onset, the valve member 35 isclosed by the electromagnetic actuating member 16. The fuel volume nowenclosed in the pump work chamber 18 is brought to high pressure andconsequently fed to one of the injection lines 21 via the pressure line19 and the distributor opening 20. To terminate the injection or definethe injection quantity, the valve member 35 is returned to the openingstate, which is done by interrupting the supply of current to theelectromagnetic actuating member 16. From this time on, the pressure inthe pump work chamber 18 can decrease toward the second valve chamber 24and from there toward the low-pressure region 45.

In FIG. 2, the embodiment according to the invention is now shown infurther detail. Once again, in FIG. 2 the guide part 37 of the valvemember 35 and the first valve chamber 36 that annularly surrounds thisvalve member 35 and is defined by the valve seat 34 on the side remotefrom the guide part 38 can be seen. Once again, the pressure conduit 46leads away from the first valve chamber 36 to the distributor opening20. The connecting line 27 of FIG. 1 is now called the connecting line127. It extends obliquely upward in the drawing in the direction of thevalve opening 33 and, with the wall toward the valve seat of the secondvalve chamber 24, forms an angle α a which is greater than 90°. In thepreferred exemplary embodiment shown here, this angle is approximately135°. The extension of the axis of the connecting line pointsapproximately through the valve opening 33 to the discharge point of thepressure conduit 46 into the first valve chamber 36. The discharge pointof the connecting line 127 into the second valve chamber is locatedapproximately halfway along the length thereof between the valve seat34, or valve sealing face 32, and the compensation piston 43. Thespecial feature in this connecting line embodied as a conduit is thatfrom an initially larger diameter, it changes over toward the secondvalve chamber 24 into a diameter constriction 57, which dischargesdirectly, with a then constant diameter, into the second valve chamber24. A transition 60 is provided between the diameter constriction 57 andthe larger-diameter part 58 of the connecting line 127; in the exampleshown, the transition is embodied pointing in funnel-like fashion towardthe second valve chamber 24. The angular version shown here may also beprovided with rounded transitions. This transition 60 and the diameterconstriction 57 may also be embodied in diffusor-like fashion, that is,with streamlined continuous transitions to the larger diameter in theoutflow direction. In all flow directions, such a diffusor furnishes astreamlined introduction of liquid.

The connecting line 127 communicates constantly with an annular groove129, which corresponds to the annular groove 29 of FIG. 1 but is nowmade in the jacket face of the cylinder line 14 and also communicatesconstantly with the low-pressure region 45. In the same way, the springchamber 23 shown in FIG. 2 has a connection 22 a shown now leading to aconduit, not shown, that leads out of the pump.

It can be seen from the section in FIG. 3 that not merely one connectingline 127 but rather three connecting lines are provided, spaced apart bythe same angles. The discharge points of the diameter constrictions 57are located in a common radial plane to the axis of the distributorshaft. One of these connecting lines 127, as can be seen here, islocated in a radial plane opposite the discharge point of the pressureconduit. These discharge points are naturally axially offset from oneanother, since they open into different valve chambers.

With this embodiment, it is attained that upon an opening of the valvemember 35, fuel flows over at high pressure out of the first valvechamber 36 into the gap between the valve sealing face 32 and the valveseat 34 into the second valve chamber 24. This flow has the tendency ofuneven distribution of the overflow speeds, which results from thegeometry of the first valve chamber 36 having the single discharge pointof the pressure conduit 46. This kind of pronounced flow profile cancause turbulence to develop inside the second valve chamber 24, which isespecially true if a quite low pressure prevails there and persists fora long time, with a large outflow cross section of the kind that may befavorable for adequate filling of the pump work chamber. However,because the diameter constriction 57 is now provided, it initially actsas a high flow resistance, before a stable outflowing fuel stream candevelop through this diameter constriction, in such a way that initiallya certain pressure level has to build up in the second valve chamber 24,by means of the fuel flowing in via the valve seat. This causes a rapidpressure buildup there and counteracts the relief of the fuel as itflows over from a high pressure level to a low pressure level, in such away that turbulent flows and isolated instances of outgassing within thesecond valve chamber 24 are avoided. Once an adequately high pressurehas built up in the second valve chamber, the stable, regular outflow offuel then occurs through the diameter constriction 57, resulting in afurther pressure relief in the region of the larger-diameter part 58 ofthe connecting line 127 toward the low-pressure region 45. As soon asthis flow has developed, at the same time the risk of formations of gasnests in the second valve chamber 24 is averted, which thus alsoprevents the risk of cavitation erosion. By uniform throttling on allsides of the outflow, as a consequence of the uniformly distributedlow-pressure lines, a symmetrical pressure buildup is promoted, whichfavors a relatively ordered flow in the low-pressure region and inparticular the formation of protective recirculation flows along thewalls of the low-pressure region, which keep outgassing components awayfrom the walls of the low-pressure region and the valve seat 34, if suchoutgassing even occurs at all.

The cross sections of the diameter constrictions are dimensioned suchthat in the filling mode of the pump work chamber, an adequate inflowcross section is available, and the pump work chamber can also beadequately intake stroke filled. The high wall portion of the inflow,which now comprises a plurality of bores, favors the initial rapidpressure buildup in the case where the pump work chamber is beingrelieved.

In this way, by a simple but effective provision, the fuel injectionpump is guarded quite substantially against possible cavitation erosion.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A fuel injection pump of the distributor type forsupplying a plurality of fuel injection valves of an internal combustionengine, comprising at least one reciprocatingly driven pump piston (17)that defines a pump work chamber (18) and upon each supply stroke pumpsfuel at injection pressure out of this pump work chamber to one of thefuel injection valves, a rotationally driven distributor shaft (11) thatupon rotation in the supply stroke of the pump piston (18) establishescommunication, via a distributor opening (20) on the circumference ofthe distributor shaft which communicates constantly with the pump workchamber, between the pump work chamber (18) and a fuel injection valve,and having an electrically controlled switching valve (16) which servesto control fuel injection over a course of the supply stroke of the pumppiston (17) and has a valve member (35) that controls a valve opening(33) between a first valve chamber (36) and a second valve chamber (24),wherein the first valve chamber (36) communicates constantly with thedistributor opening (20) via a pressure conduit (46) and a connectingline (127) leads from the second valve chamber (24) to a fuel-filledlow-pressure chamber (45) and both the filling and relieving of the pumpwork chamber (18) are effected via this connecting line (127), thesecond valve chamber (24) adjoins a valve seat (34) of the valve member(35) and is disposed in the distributor shaft (11) coaxially to the axisof the distributor shaft, and the connecting line (127) has a diameterconstriction (57).
 2. The fuel injection pump according to claim 1, inwhich the connecting line (127) leads away from the second valve chamber(24) in such a way that with a part of a wall of the distributor shafttoward the valve seat, of the second valve chamber the connecting lineforms an angle greater than 90°.
 3. The fuel injection pump according toclaim 2, in which a transition, located to a side of the low-pressureregion (45), between the diameter constriction (57) and thelarger-diameter part (58) of the connecting line (127) narrows infunnel-like fashion toward the second valve chamber (24).
 4. The fuelinjection pump according to claim 2, in which three connecting lines(127) are provided, with outlet openings located in a common radialplane to one of the axis of the distributor shaft (11) and the secondvalve chamber (24) and are spaced apart by equal angles from oneanother.
 5. The fuel injection pump according to claim 2, in which thesecond valve chamber (24) on a side remote from the valve seat (34) isdefined by a compensation piston (43), which is connected to the valveclosing member (35) via a connecting tang (56) and on another sideadjoins a pressure-relieved chamber (23).
 6. The fuel injection pumpaccording to claim 1, in which a transition, located to a side of thelow-pressure region (45), between the diameter constriction (57) and thelarger-diameter part (58) of the connecting line (127) narrows infunnel-like fashion toward the second valve chamber (24).
 7. The fuelinjection pump according claim 6, in which the transition is providedwith rounded transition regions.
 8. The fuel injection pump according toclaim 7, in which a diameter of the constriction (57) dischargesdirectly into the second valve chamber (24).
 9. The fuel injection pumpaccording to claim 6, in which the transition pointing toward thelow-pressure side is a diffusor.
 10. The fuel injection pump accordingto claim 9, in which a diameter of the constriction (57) dischargesdirectly into the second valve chamber (24).
 11. The fuel injection pumpaccording to claim 6, in which a diameter of the constriction (57)discharges directly into the second valve chamber (24).
 12. The fuelinjection pump according to claim 6, in which three connecting lines(127) are provided, with outlet openings located in common radial planeto one of the axis of the distributor shaft (11) and the second valvechamber (24) and are spaced apart by equal angles from one another. 13.The fuel injection pump according to claim 2, in which the second valvechamber (24) on a side remote from the valve seat (34) is defined by acompensation piston (43), which is connected to the valve closing member(35) via a connecting tang (56) and on another side adjoins apressure-relieved chamber (23).
 14. The fuel injection pump according toclaim 1, in which a plurality of connecting lines (127) distributed overthe circumference of the second valve chamber (24) lead away from thesecond valve chamber.
 15. The fuel injection pump according to claim 14,in which the connecting lines (127) are spaced apart by equal anglesfrom one another.
 16. The fuel injection pump according to claim 15, inwhich one of the connecting lines (127) is located in a radial plane,opposite the pressure conduit (46) leading away from the first valvechamber (36).
 17. The fuel injection pump according to claim 1, in whichthree connecting lines (127) are provided, with outlet openings locatedin common radial plane to one of the axis of the distributor shaft (11)and the second valve chamber (24) and are spaced apart by equal anglesfrom one another.
 18. A fuel injection pump according to claim 1, inwhich the valve member (35) is a seat valve, with a valve seat (34)oriented toward the first valve chamber (36).
 19. The fuel injectionpump according to claim 1, in which the second valve chamber (24) on aside remote from the valve seat (34) is defined by a compensation piston(43), which is connected to the valve closing member (35) via aconnecting tang (56) and on another side adjoins a pressure-relievedchamber (23).
 20. The fuel injection pump according to claim 19, inwhich the valve chamber (35) is urged in an opening direction by acompression spring (44), and the compression spring engages a side ofthe compensation piston (43) remote from the second valve chamber (24).